The computer, information, and entertainment industries produce and consume annually hundreds of millions of disk-shaped substrates, principally silicon wafers, and aluminum, plastic, glass, or other multi-component disks. In the fabrication of computer CPU chips, silicon wafers are processed through multiple fabrication steps which include repeated application and selective removal of variously conductive, non-conductive and semi-conductive materials before the resulting micro-circuits are complete and separated into individual dies. Aluminum, glass, and other composite disk substrates are typically over-coated with magnetic, optical, or magneto-optical materials in the fabrication of HDDs, CDs, DVDs, and other data storage products.
Substrates must be buffed, polished, etched, cleaned, and otherwise prepared repeatedly during the fabrication process. This is true for both wafer and disk substrates. In the semiconductor manufacturing industry, integrated circuit devices designed with complex, and extremely fine and precise multi-layered structures, require highly clean and prepared surfaces. In the field of magnetic and optical media disks, ever-increasing areal density translates into exacting requirements for disk cleaning and preparation. Defects resulting from improper, incomplete, or insufficient substrate buffing, polishing, cleaning, or other preparation produces decreased yield and increased time and cost.
By way of example, a microscopic contaminant of size on the order of 0.1 micron left on the surface of a hard drive disk substrate could cause the hard drive to fail, as the clearance between the drive head and the substrate magnetic media is only on the order of 0.0125 microns (0.5 microinches). Accordingly, the standard of cleanliness of hard drive substrates currently required in industry is no more than 1 particle per side no greater than 0.1 micron. More contaminants in size or number result in rejection of the substrate disk and a reduction in yield. This is extremely significant in this industry, as the cost to the consumer per megabyte of hard drive capacity, on the order of $40 per MB in 1985, is now on the order of <0.125 cents per MB, or <$1.25 per Gigabyte. With incredibly thin margins, it becomes essential that substrate cleaning systems, e.g., scrubber apparatus and methods, are fast, highly efficient and result in high yield of substrates that meet particulate cleanliness standards.
To meet the ever increasing demands for cleaner substrates, both semiconductor and disk industries adopted rotating brush scrubbing as the standard cleaning procedure. Each brush station includes one or more pair of brushes. The brush material is usually polyvinyl alcohol (PVA), but other materials such as mohair and nylon can be used. To keep the brushes clean and extend the brush life, it is common practice to deliver water or other cleaning fluid through a hollow brush core. The brush core has a one open end for cleaning fluid input. The cleaning fluid is delivered from the interior of the brush core to the interface of the PVA brush and substrate surface being cleaned through as series of fine holes or channels distributed along the longitudinal length of the brush and passing through the wall of the brush. The open end of the brush core is coupled with a supply housing that provides cleaning fluid under pressure that continuously passes through the holes and flushes the interface of the brush with the substrate surface being cleaned.
However, in present commercially available brush scrubber systems, the cleaning/rinsing fluid supply is connected to the hollow brushes via a double ring bearing. During the cleaning operation the water pressure pushes an axially slideable delivery piston or nozzle of the cleaning fluid supply housing against the rotating brush core in order to maintain a positive seal against the fluid pressure. The piston is slideable to permit removal of the brush. The resulting contact under pressure causes wear on both the contacting bodies (bearing and brush mandrel) resulting in microparticle debris generation. This wear-generated debris will migrate with cleaning fluid through the brush holes or channels to the substrate surface. The debris results in product failure and yield loss through, for example, scoring of the substrate surface or deposition on the surface. The result is that current brush scrubber systems are rapidly approaching efficiency limits, in that they can actually produce particulates rather than remove them.
Accordingly, there is a need in the art for a cleaning system that can keep up with the increasing requirements for substrate cleanliness, and more particularly a system that includes fluid delivery assemblies that reduce the potential for contribution of particulate debris during the cleaning process, and that is simple and inexpensive to manufacture and maintain.